Optical link management

ABSTRACT

The present disclosure provides optical link management in a marine seismic environment. A first device can transmit, to a second device, a first optical transmission at a first output level. The first optical transmission can include a first packet corresponding to a network protocol. The first device can determine that the second device failed to receive the first packet via the first optical transmission. The first device can transmit, responsive to failure of the first optical transmission, a second optical transmission at a second output level different than the first output level. The second optical transmission can include a second packet corresponding to the network protocol. The first device can identify that the second packet was successfully received by the second link manager agent. The first device can establish, responsive to the identification that the second packet was successfully received, the second output level as a transmission output level for the first device.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. § 119 ofU.S. Provisional Patent Application No. 62/328,417 filed Apr. 27, 2016,which is incorporated by reference herein in its entirety.

BACKGROUND

Seismic data may be evaluated to obtain information about subsurfacefeatures. The information can indicate geological profiles of asubsurface portion of earth, such as salt domes, bedrock, orstratigraphic traps, and can be interpreted to indicate a possiblepresence or absence of minerals, hydrocarbons, metals, or other elementsor deposits. Devices can communicate the seismic data using acommunication link. However, due to environmental variables, it may bechallenging to manage the communication link between the devices.

SUMMARY

The present disclosure is generally directed to systems and methodsconfigured with techniques to manage an optical communications link in afree-space. Managing an optical communications link can include or referto establishing the optical communications link between two or moredevices, and maintaining the optical communications link between the twoor more devices.

At least one aspect is directed to a system to manage an optical link tocommunicate data via an aqueous medium. The system can include a firstlink manager agent of a first device. The first link manager agent cantransmit, to a second link manager agent of a seismic data acquisitiondevice, a first optical transmission at a first output level. The firstoptical transmission can include a first packet corresponding to anetwork protocol. The first link manager agent can determine that thesecond link manager agent failed to receive the first packet via thefirst optical transmission. The first link manager agent can transmit,responsive to failure of the first optical transmission, a secondoptical transmission at a second output level different, greater than orless than the first output level. The second optical transmission caninclude a second packet corresponding to the network protocol. The firstlink manager agent can identify that the second packet was successfullyreceived by the second link manager agent. The first link manager agentcan establish, responsive to the identification that the second packetwas successfully received, the second output level as a transmissionoutput level for the seismic data acquisition device.

At least one aspect is directed to a method of managing an optical linkto communicate data via an aqueous medium. The method can include afirst link manager agent of a first device transmitting a first opticaltransmission at a first output level to a second link manager agent of aseismic data acquisition device. The first optical transmission caninclude a first packet corresponding to a network protocol. The methodcan include the first link manager agent determining that the secondlink manager agent failed to receive the first packet via the firstoptical transmission. The method can include the first link manageragent transmitting, responsive to failure of the first opticaltransmission, a second optical transmission at a second output leveldifferent, greater than or less than the first output level. The secondoptical transmission can include a second packet corresponding to thenetwork protocol. The method can include the first link manager agentidentifying that the second packet was successfully received by thesecond link manager agent. The method can include the first link manageragent establishing, responsive to determining that the second packet wassuccessfully received, the second output level as a transmitting outputlevel for the seismic data acquisition device.

At least one aspect is directed to a method of managing an optical linkto communicate data via an aqueous medium. The method can include afirst link manager agent of a device identifying an optical linkestablished with a first output level between the device and a secondlink manager agent of a seismic data acquisition device. The method caninclude the first link manager agent transmitting, to the second linkmanager agent of the seismic data acquisition device, a first opticaltransmission at a first output level. The first optical transmission caninclude a first packet corresponding to a network protocol. The methodcan include the first link manager agent determining that the secondlink manager agent failed to receive the first packet via the firstoptical transmission. The method can include the first link manageragent transmitting, responsive to failure of the first opticaltransmission, a second optical signal at a second output level greaterthan the first output level. The second optical transmission can includea second packet corresponding to the network protocol. The method caninclude the first link manager agent identifying that the second packetwas successfully received by the second link manager agent. The methodcan include the first link manager agent adjusting, responsive to adetermination of successful receipt of the second packet, the opticallink to use the second output level for optical transmissions betweenthe device and the seismic data acquisition device.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. Likereference numbers and designations in the various drawings indicate likeelements. For purposes of clarity, not every component may be labeled inevery drawing. In the drawings:

FIG. 1 depicts an isometric schematic view of an embodiment of a seismicoperation in deep water.

FIG. 2 is an embodiment of a system to manage an optical communicationlink in free-space.

FIG. 3 is an embodiment of a system to manage an optical communicationlink in free-space.

FIG. 4 depicts a method for managing an optical communication link infree-space.

FIG. 5 depicts a block diagram of an architecture for a computing systememployed to implement various elements of the system depicted in FIGS.1, 2 and 3, and perform the method depicted in FIG. 4.

DETAILED DESCRIPTION

The present disclosure is directed to systems and methods for managingan optical communications link in free-space. Managing an opticalcommunications link can include or refer to establishing the opticalcommunications link between two or more devices, and maintaining theoptical communications link between the two or more devices. Acommunication link in free-space can refer to, for example, anycommunication that is, at least in part, not conveyed via a fiber, wireor other physical conduit. For example, a communication link infree-space can include an optical communication through a medium such asair or an ocean water, sea water, lake water or other aqueous medium orfluid.

To manage an optical communication link in free-space, the presentdisclosure provides devices including a link manager agent that canmanage an optical link. The devices can be configured with a half-duplextechnique that allows an optical transmitter and receiver pair tounilaterally identify a gain level that allows the optical transmitterand optical receiver to parse or process optical signals to retrieve theinformation carried by the optical signals. The devices can establishthe communication link using a lower level link management technique todetermine whether all the bits in a frame were received. The devices canbe further configured to maintain the communication link using a higherlevel link management technique to determine whether there were anyerrors in a data packet and, if so, re-request the data packet.

Systems and methods of the present disclosure can use non-standard bitrates, such as 320 megabits per second (mbps). The system can use orselect a bit rate based on a clock control rate and circuit design ofone or more components of the devices.

For example, a device including the link manager agent can receive aninitial wake-up signal in the form of an optical communication, such aslight, light pulse, illumination, luminescence or other visualindicator. The device can include a receiver automatic gain control(“AGC”) unit that can determine whether the incoming wake-up signal (oroptical signals or communications received subsequent to the wake-upsignal) is above or below a threshold (e.g., an intensity or strength ofthe optical signal is above or below a predetermined threshold). If thereceiver AGC unit determines the signal is below the threshold (e.g.,having an intensity below the threshold), such as too low to reliabledetermine the information carried via the optical signal, then thereceiver AGC unit can increase a gain to amplify the signal. If thereceiver AGC unit determines the signal is too bright (e.g., having anintensity above the threshold), the receiver AGC unit can decrease orreduce the gain. The receiver AGC can provide self-preservation for oneor more component of the device to prevent or reduce damage caused tohardware, such as optical components of the device, fiber optics of thedevice, or other photoelectric or electronic components. Theself-preservation can also reduce heat output by components, such as aphotodetector or battery that is powering one or more component of thedevice.

The receiver AGC unit, responsive to receiving the initial wake-upsignal instructing the device to wake-up or enter an on state, canincrease a gain of the device until the device can detect the opticalsignal and retrieve information carried by the optical signal.

In some cases, a first device can have a first link manager agent and asecond device can have a second link manager agent. The link manageragents can control one or more parameters or components of theirrespective device, such as an optical transmitter, optical receiver,transmit output level, or AGC unit. For example, to establish andmaintain the optical communications link in free space, the first linkmanager agent can select a transmit output level for an opticaltransmitter based on one or more variables associated with an opticalreceiver that is to receive the output transmitted by the opticaltransmitter. However, in free space optical systems, one or morevariables can affect the optical communications link or the process ofselecting a transmit output level, such as absorption, scattering,alignment, distance between the optical transmitter and thecorresponding optical receiver, or motion related to the devices or linkmanager agents. Thus, to produce a robust optical communications link,the link manager agent can evaluate various information.

The optical communication link can be used to transfer, harvest, collector otherwise communicate data, including data related to oilfieldoperations, oil exploration, hydrocarbon production, hydrocarbonexploration, marine seismic activity, or ocean field operations. Thedata can be transferred to an underwater vehicle from a sensor via theoptical communications link. The sensor can include a seismic sensordevice or other sensors or devices such as environmental sensors thatdetect pressure, temperature, flow, vibration, power source condition,water motion, or other environmental factors. The data can betransferred, harvested, or otherwise collected using the opticalcommunications link based on a time interval (e.g., every 1 hour, 2hours, 5 hours, 12 hours, 24 hours, 48 hours, or 72 hours), responsiveto an event (e.g., after an acoustic shot), or responsive to aninstruction to collect the information.

FIG. 1 is an isometric schematic view that illustrates a non-limitingexample of an embodiment of a seismic operation. The seismic operationcan be in deep water and facilitated by a first marine vessel 5. Thefirst vessel 5 is positioned on a surface 10 of a water column 15 andincludes a deck 20 which supports operational equipment. At least aportion of the deck 20 includes space for a plurality of sensor deviceracks 90 where seismic sensor devices are stored. The sensor deviceracks 90 may also include data retrieval devices or sensor rechargingdevices.

The deck 20 also includes one or more cranes 25A, 25B attached theretoto facilitate transfer of at least a portion of the operationalequipment, such as an ROV or seismic sensor devices, from the deck 20 tothe water column 15. For example, a crane 25A coupled to the deck 20 isconfigured to lower and raise an ROV 35A, which transfers and positionsone or more sensor devices 30 on a seabed 55. The seabed 55 can includea lakebed 55, ocean floor 55, or earth 55. The ROV 35A can be wireless.The ROV 35A can be self-contained. The ROV 35A can be coupled to thefirst vessel 5 by, for example, a tether 46A and an umbilical cable 44Athat provides power, communications, and control to the ROV 35A. Atether management system (TMS) 50A can be coupled between the umbilicalcable 44A and the tether 46A. The TMS 50A may be utilized as anintermediary, subsurface platform from which to operate the ROV 35A. Insome cases, for ROV 35A operations at or near the seabed 55, the TMS 50Acan be positioned approximately 50 feet above seabed 55 and can pay outtether 46A for ROV 35A to move freely above seabed 55 to position andtransfer seismic sensor devices 30 thereon. Sensor device 30 can includea seismic sensor device or non-seismic sensor devices, as well ascombinations thereof.

A crane 25B may be coupled (e.g., via a latch, anchor, nuts and bolts,screw, suction cup, magnet, or other fastener) to a stern of the firstvessel 5, or other locations on the first vessel 5. Each of the cranes25A, 25B may be any lifting device or launch and recovery system (LARS)adapted to operate in a marine environment. The crane 25B can be coupledto a seismic sensor transfer device 100 by a cable 70. The transferdevice 100 may be a drone, a skid structure, a basket, or any devicecapable of housing one or more sensor devices 30 therein. The transferdevice 100 may be a structure configured as a magazine adapted to houseand transport one or more sensor devices 30. The transfer device 100 canbe configured as a sensor device storage rack for transfer of sensordevices 30 from the first vessel 5 to the ROV 35A, and from the ROV 35Ato the first vessel 5. The cable 70 may be an umbilical, a tether, acord, a wire, a rope, and the like, that is configured to support thetransfer device 100.

The ROV 35A can include a seismic sensor device storage compartment 40that is configured to store one or more seismic sensor devices 30therein for a deployment or retrieval operation. The storage compartment40 may include a magazine, a rack, or a container configured to storethe seismic sensor devices. The storage compartment 40 may also includea conveyor, such as a movable platform having the seismic sensor devicesthereon, such as a carousel or linear platform configured to support andmove the seismic sensor devices 30 therein. The seismic sensor devices30 may be deployed on the seabed 55 and retrieved therefrom by operationof the movable platform. The ROV 35A may be positioned at apredetermined location above or on the seabed 55 and seismic sensordevices 30 are rolled, conveyed, or otherwise moved out of the storagecompartment 40 at the predetermined location. In some embodiments, theseismic sensor devices 30 may be deployed and retrieved from the storagecompartment 40 by a robotic device 60, such as a robotic arm, an endeffector or a manipulator, disposed on the ROV 35A.

The seismic sensor device 30 may include a sensor in an oil productionfield, and can be a seismic data acquisition unit or node. The seismicsensor device 30 can record seismic data. Seismic data can include, forexample, data collected by the one or more sensors of the device 30 suchas trace data, force data, motion data, pressure data, vibration data,electrical current or voltage information indicative of force orpressure, temperature data, or tilt information. The seismic sensordevice 30 may include one or more of at least one motion detector suchas a geophone, at least one pressure detector such as a hydrophone, atleast one power source (e.g., a battery, external solar panel), at leastone clock, at least one tilt meter, at least one environmental sensor,at least one seismic data recorder, at least one global positioningsystem sensor, at least one wireless or wired transmitter, at least onewireless or wired receiver, at least one wireless or wired transceiver,or at least one processor. The seismic sensor device 30 may be aself-contained unit such that all electronic connections are within theseismic sensor device 30, or one or more components can be external tothe seismic sensor device 30. During recording, the seismic sensordevice 30 may operate in a self-contained manner such that the node doesnot require external communication or control. The seismic sensor device30 may include several geophones and hydrophones configured to detectacoustic waves that are reflected by subsurface lithological formationor hydrocarbon deposits. The seismic sensor device 30 may furtherinclude one or more geophones that are configured to vibrate the seismicsensor device 30 or a portion of the seismic sensor device 30 in orderto detect a degree of coupling between a surface of the seismic sensordevice 30 and a ground surface. One or more component of the seismicsensor device 30 may attach to a gimbaled platform having multipledegrees of freedom. For example, the clock may be attached to thegimbaled platform to minimize the effects of gravity on the clock.

The device 30 can include or refer to other types of sensors or unitsused in oilfield or hydrocarbon operations, production or exploration.The device 30 can record, detector, collect or obtain data related tooil field production or hydrocarbon production. The device 30 cancollect data related to oil field production or hydrocarbon productionthat includes, for example, pressure information (e.g., pressure of oilor other fluid flowing through a pipe), temperature data (e.g., ambienttemperature, temperature of a fluid flowing through a pipe, ortemperature of a component or device), current flow (e.g., water flow orrate in an aqueous medium, river or ocean).

For example, in a deployment operation, a first plurality of seismicsensor devices, comprising one or more sensor devices 30, may be loadedinto the storage compartment 40 while on the first vessel 5 in apre-loading operation. The ROV 35A, having the storage compartmentcoupled thereto, is then lowered to a subsurface position in the watercolumn 15. The ROV 35A can utilize commands from personnel on the firstvessel 5 to operate along a course to transfer the first plurality ofseismic sensor devices 30 from the storage compartment 40 and deploy theindividual sensor devices 30 at selected locations on the seabed 55.Once the storage compartment 40 is depleted of the first plurality ofseismic sensor devices 30, the transfer device 100 is used to ferry asecond plurality of seismic sensor devices 30 as a payload from firstvessel 5 to the ROV 35A.

The transfer system 100 may be preloaded with a second plurality ofseismic sensor devices 30 while on or adjacent the first vessel 5. Whena suitable number of seismic sensor devices 30 are loaded onto thetransfer device 100, the transfer device 100 may be lowered by crane 25Bto a selected depth in the water column 15. The ROV 35A and transferdevice 100 are mated at a subsurface location to allow transfer of thesecond plurality of seismic sensor devices 30 from the transfer device100 to the storage compartment 40. When the transfer device 100 and ROV35A are mated, the second plurality of seismic sensor devices 30contained in the transfer device 100 are transferred to the storagecompartment 40 of the ROV 35A. Once the storage compartment 40 isreloaded, the ROV 35A and transfer device 100 are detached or unmatedand seismic sensor device placement by ROV 35A may resume. Reloading ofthe storage compartment 40 can be provided while the first vessel 5 isin motion. If the transfer device 100 is empty after transfer of thesecond plurality of seismic sensor devices 30, the transfer device 100may be raised by the crane 25B to the vessel 5 where a reloadingoperation replenishes the transfer device 100 with a third plurality ofseismic sensor devices 30. The transfer device 100 may then be loweredto a selected depth when the storage compartment 40 is reloaded. Thisprocess may repeat as until a desired number of seismic sensor devices30 have been deployed.

Using the transfer device 100 to reload the ROV 35A at a subsurfacelocation can reduce the time required to place the seismic sensordevices 30 on the seabed 55, or “planting” time, as the ROV 35A is notraised and lowered to the surface 10 for seismic sensor devicereloading. Further, mechanical stresses placed on equipment utilized tolift and lower the ROV 35A are minimized as the ROV 35A may be operatedbelow the surface 10 for longer periods. The reduced lifting andlowering of the ROV 35A may be particularly advantageous in foul weatheror rough sea conditions. Thus, the lifetime of equipment may be enhancedas the ROV 35A and related equipment are not raised above surface 10,which may cause the ROV 35A and related equipment to be damaged, or posea risk of injury to the vessel personnel.

The sensor devices 30 can be placed on seabed 55 for an extendedduration, such as 1 year, 2 years, 3 years, 4 years, 5 years, or more.Data, such as seismic data or status data, can be retrieved from thesensor devices 30 while they are located on the seabed 55 using wirelesstransmission techniques, such as optical links.

In a retrieval operation, the ROV 35A can utilize commands frompersonnel on the first vessel 5 to retrieve each seismic sensor device30 that was previously placed on seabed 55. The retrieved seismic sensordevices 30 are placed into the storage compartment 40 of the ROV 35A. Insome embodiments, the ROV 35A may be sequentially positioned adjacenteach seismic sensor device 30 on the seabed 55 and the seismic sensordevices 30 are rolled, conveyed, or otherwise moved from the seabed 55to the storage compartment 40. In some embodiments, the seismic sensordevices 30 may be retrieved from the seabed 55 by a robotic device 60disposed on the ROV 35A.

Once the storage compartment 40 is full, contains a pre-determinednumber of seismic sensor devices 30, or is otherwise ready, the transferdevice 100 is lowered to a position below the surface 10 and mated withthe ROV 35A. The transfer device 100 may be lowered by crane 25B to aselected depth in the water column 15, and the ROV 35A and transferdevice 100 are mated at a subsurface location. Once mated, the retrievedseismic sensor devices 30 contained in the storage compartment 40 aretransferred to the transfer device 100. Once the storage compartment 40is depleted of retrieved sensor devices, the ROV 35A and transfer device100 are detached and sensor device retrieval by ROV 35A may resume.Thus, the transfer device 100 is used to ferry the retrieved seismicsensor devices 30 as a payload to the first vessel 5, allowing the ROV35A to continue collection of the seismic sensor devices 30 from theseabed 55. In this manner, sensor device retrieval time is significantlyreduced as the ROV 35A is not raised and lowered for sensor deviceunloading. Further, safety issues and mechanical stresses placed onequipment related to the ROV 35A are minimized as the ROV 35A may besubsurface for longer periods.

The first vessel 5 may travel in a first direction 75, such as in the +Xdirection, which may be a compass heading or other linear orpredetermined direction. The first direction 75 may also account for orinclude drift caused by wave action, current(s) or wind speed anddirection. In one embodiment, the plurality of seismic sensor devices 30are placed on the seabed 55 in selected locations, such as a pluralityof rows Rn in the X direction (R1 and R2 are shown) or columns Cn in theY direction (C1-Cn are shown), wherein n equals an integer. In oneembodiment, the rows Rn and columns Cn define a grid or array, whereineach row Rn (e.g., R1-R2) comprises a receiver line in the width of asensor array (X direction) or each column Cn comprises a receiver linein a length of the sensor array (Y direction). The distance betweenadjacent sensor devices 30 in the rows is shown as distance LR and thedistance between adjacent sensor devices 30 in the columns is shown asdistance LC. While a substantially square pattern is shown, otherpatterns may be formed on the seabed 55. Other patterns includenon-linear receiver lines or non-square patterns. The pattern(s) may bepre-determined or result from other factors, such as topography of theseabed 55. The distances LR and LC may be substantially equal and mayinclude dimensions between about 60 meters to about 400 meters, orgreater. The distance between adjacent seismic sensor devices 30 may bepredetermined or result from topography of the seabed 55 as describedabove.

The first vessel 5 can be operated at a speed, such as an allowable orsafe speed for operation of the first vessel 5 and any equipment beingtowed by the first vessel 5. The speed may take into account any weatherconditions, such as wind speed and wave action, as well as currents inthe water column 15. The speed of the vessel may also be determined byany operations equipment that is suspended by, attached to, or otherwisebeing towed by the first vessel 5. For example, the speed can be limitedby the drag coefficients of components of the ROV 35A, such as the TMS50A and umbilical cable 44A, as well as any weather conditions orcurrents in the water column 15. As the components of the ROV 35A aresubject to drag that is dependent on the depth of the components in thewater column 15, the first vessel speed may operate in a range of lessthan about 1 knot. In this embodiment, wherein two receiver lines (rowsR1 and R2) are being laid, the first vessel includes a first speed ofbetween about 0.2 knots and about 0.6 knots. In other embodiments, thefirst speed includes an average speed of between about 0.25 knots, whichincludes intermittent speeds of less than 0.25 knots and speeds greaterthan about 1 knot, depending on weather conditions, such as wave action,wind speeds, or currents in the water column 15.

During a seismic survey, one receiver line, such as row R1 may bedeployed. When the single receiver line is completed a second vessel 80is used to provide a source signal. The second vessel 80 is providedwith a source device or acoustic source device 85, which may be a devicecapable of producing acoustical signals or vibrational signals suitablefor obtaining the survey data. The source signal propagates to theseabed 55 and a portion of the signal is reflected back to the seismicsensor devices 30. The second vessel 80 may be required to make multiplepasses, for example at least four passes, per a single receiver line(row R1 in this example). During the time the second vessel 80 is makingthe passes, the first vessel 5 continues deployment of a second receiverline. However, the time involved in making the passes by the secondvessel 80 may be much shorter than the deployment time of the secondreceiver line. This causes a lag time in the seismic survey as thesecond vessel 80 sits idle while the first vessel 5 is completing thesecond receiver line.

The first vessel 5 can use one ROV 35A to lay sensor devices to form afirst set of two receiver lines (rows R1 and R2) in any number ofcolumns, which may produce a length of each receiver line of up to andincluding several miles. The two receiver lines (rows R1 and R2) can beparallel or substantially parallel (e.g., less than 1 degree, 2 degrees,0.5 degrees, 0.1 degrees, or 5 degrees). When a single directional passof the first vessel 5 is completed and the first set (rows R1, R2) ofseismic sensor devices 30 are laid to a predetermined length, the secondvessel 80, provided with the source device 85, is utilized to providethe source signal. The second vessel 80 can make eight or more passesalong the two receiver lines to complete the seismic survey of the tworows R1 and R2.

While the second vessel 80 is shooting along the two rows R1 and R2, thefirst vessel 5 may turn 180 degrees and travel in the X direction inorder to lay seismic sensor devices 30 in another two rows adjacent therows R1 and R2, thereby forming a second set of two receiver lines. Thesecond vessel 80 may then make another series of passes along the secondset of receiver lines while the first vessel 5 turns 180 degrees totravel in the +X direction to lay another set of receiver lines. Theprocess may repeat until a specified area of the seabed 55 has beensurveyed. Thus, the idle time of the second vessel 80 is minimized asthe deployment time for laying receiver lines is cut approximately inhalf by deploying two rows in one pass of the vessel 5.

Although only two rows R1 and R2 are shown, the sensor device 30 layoutis not limited to this configuration as the ROV 35A may be adapted tolayout more than two rows of sensor devices in a single directional tow.For example, the ROV 35A may be controlled to lay out between three andsix rows of sensor devices 30, or an even greater number of rows in asingle directional tow. The width of a “one pass” run of the firstvessel 5 to layout the width of the sensor array can be limited by thelength of the tether 46A or the spacing (distance LR) between sensordevices 30.

FIG. 2 is an embodiment of a system to manage an optical communicationlink in free-space. The system 200 can include one or more devices 205and 255. The devices 205 and 255 can include or refer to a seismic dataacquisition device 30, seismic sensor device 30, an ocean bottom seismicdata acquisition unit, seismic sensor device 30, a geophone, ahydrophone, ROV 35A, autonomous underwater vehicle 35A, or underwatervehicle 35A. The system 200 can include one or more component, elementor functionality of system 300 depicted in FIG. 3.

The devices 205 and 255 can include one or more of at least onetransmitter 210, at least one receiver 215, at least one link manageragent 220, at least one gain control unit 225, at least one overdriveprotection system 230, or at least one data storage device 235. The datastorage device 235 can include memory, storage, a database, datastructures, or a file repository. The data storage device 235 can storeor maintain one or more of seismic data 240, output level 245, orprotocols 250. The transmitter 210, receiver 215, link manager agent220, gain control unit 225, overdrive protection system 230 and datastorage device 235 can communicate or interface with one anotherdirectly (e.g., via wired or wireless communication) or indirectly(e.g., via another component of system 200). The system 200 and itscomponents, including device 205 and 255, may include hardware elements,such as one or more processors, logic devices, or circuits. For example,the first device 205 can include one or more subcomponents to transmit afirst optical transmission at a first output level, determine that asecond link manager agent failed to receive the first packet via thefirst optical transmission, transmit a second optical transmission at asecond output level different, less than or greater than the firstoutput level, identify that the second packet was successfully receivedby the second link manager agent, and establish the second output levelas a transmission output level for the first seismic data acquisitiondevice.

The devices 205 and 255 can include at least one logic device such as acomputing device having a processor to communicate via a communicationlink 260. The devices 205 and 255 can include a network interface, fieldprogrammable gate array, or other components or logic structures tomanage an optical link between the devices. The communication link 260can be a wireless communication link, such as an optical link infree-space.

The device 205 or 255 can include a transmitter 210. The transmitter 210can include an optical transmitter. The optical transmitter 210 caninclude, for example, a light source such as a laser light source, solidstate laser, vertical cavity surface-emitting lasers, light emittingdiode (“LED”), lamp, fluorescent light source, or incandescent lightsource. The optical transmitter 210 can include one or more lensesconfigured to form a light beam from the light emitted from the lightsource. The optical transmitter 210 can include electronic circuitry ora driver configured to provide power to the light source to transmitlight with one or more parameters. Parameters can include, for example,frequency, wavelength, intensity of light or output level, pulse rate,burst rate, or color. The optical transmitter 210 can convert electricalsignal into an optical form, and transmit the generated optical form orsignal into free-space. In some cases, the optical transmitter 210 caninclude an optical source, electrical pulse generator or opticalmodulator. The optical transmitter 210 can be positioned within thedevice 205 or adjacent to the device 205 or on an external surface ofdevice 205 such that light emitted from the optical transmitter cantravel through free-space from the first device 205 to the second device255.

The device 205 or 255 can include a receiver 215. The receiver 215 caninclude an optical receiver 215 such as a photodetector or othercomponent configured to receive light and convert or translate thereceived light into an electrical signal. The receiver 215 can include aphotodetector or photodiode that loses electrons when struck by a photonmoving at a predetermined wavelength. When the photodiode is struck bylight energy, electrons are released to create an electric charge thatthe receiver 215 can then amplify. When the signal is sufficientlyamplified, the receiver 215 can translate the signal into electricalinformation, such as digital ones and zeros.

The device 205 or 255 can include a link manager agent 220. The linkmanager agent can include one or more component or functionality ofsystem 300 depicted in FIG. 3, including, for example, link manageragent 305 network stacks 340 or 365, or FPGAs 345 or 370. The linkmanager agent 220 can instruct the optical transmitter 210 to transmitan optical transmission at an output level (e.g., light intensitylevel). The link manager 220 can encode information into an electricalsignal and provide the electrical signal to the optical transmitter 210to translate the electrical signal into light and transmit the lightthrough free-space. The link manager agent 220 can encode informationsuch as a data packet. The data packet can be encoded in accordance witha protocol 250 stored in data storage 235. The protocol 250 can includeany type of network protocol or other data transmission protocol. Theprotocol 250 used to encode the information or create a data structurefor the data packet can include, for example, a user datagram protocol(UDP), Internet protocol, transmission control protocol (TCP), or streamcontrol transmission protocol (SCTP). For example, the data packet caninclude a structure that corresponds to a user datagram protocol, suchas a number, type or size of header fields or payload. The link manageragent 220 can use a protocol 250 without handshaking to performerror-checking and correction to avoid this processing at the networkinterface level. UDP, for example, can permit individual packets to bedropped.

The first device 205 can transmit the first optical transmission at afirst output level. The first output level can refer to a default orinitial output level. The default output level can be stored in anoutput level data structure or data field stored in data storage device235. Default output levels can include an output level of a parametersuch as light intensity. Output levels 245 can be stored in data storagedevice 235 as a scale (e.g., low, medium, high), grade (e.g., A, B, C,D), or numeric scale (e.g., 1 to 10; 1 to 100 or other numeric scalewhere the ends of the scale represent high or low). The output leveldata structure 245 can include a table with multiple output levels, suchas a first output level, second output level, third output level, fourthoutput level, or fifth output level. These output levels can map to anintensity level or electric current or voltage level, power level, orother level. In some cases, the output level 245 can include numericlight intensity values or luminous intensity (e.g., candela, opticalpower per unit area, or Watts per square meter) or electrical signal(e.g., voltage or current) values. The output level can increase ordecrease based on a pattern or wave shape, such as a triangle wavepattern, sinusoidal wave, ramp function, or other wave shape or pattern.

The first device 205 can transmit the first optical transmission tofree-space or towards a second device 255. For example, the first device205 can be included with an underwater vehicle such as an ROV 35A, AUV,or vessel. The second device 205 can be included with a seismic sensordevice 30. The first device 205, upon transmitting the first opticaltransmission, can determine whether the second device 255 received thefirst optical transmission. The first device 205 can determine whetherthe second device 255 received the data packet or other informationcarried by, or encoded in, the first optical transmission. In somecases, the first device 205 can determine that the second device 255failed to receive the data packet in the first optical transmission. Insome cases, the first device 205 can determine that the second device255 successfully received the data packet carried via the opticaltransmission.

The first device 205 (or link manager agent 220) can determine that thesecond device 255 failed to receive the first packet via the firstoptical transmission. The first link manager agent 220 of the firstdevice 205 can determine that the second link manager agent failed toreceive the first packet via the first optical transmission based oninformation or light received by the first device 205 from the seconddevice 255. For example, the second device 255 can output opticaltransmission at a predetermined interval, time period, or pulserepetition frequency or pulse repetition interval (e.g., 0.1milliseconds, 0.2 milliseconds, 0.5 milliseconds, 10 milliseconds, 1second or some other time interval). The second device 255 can transmitthe optical transmissions at a default or initial time interval whichcan indicate, to the first device 205, that the second device did notsuccessfully receive the data packet in the first optical transmission.If the second device 255 successfully received the first data packet inthe first optical transmission, the second device 255 can alter aparameter of the optical transmissions, such as a pulse repetitionfrequency.

The first device 205 can detect a pulse repetition interval or othertime interval of the optical transmission sent by the second device 255.The first device 205 can determine that the pulse repetition intervalcorresponds to a predetermined pulse repetition interval that indicatesthat the second device 255 did not successfully receive one or more datapacket sent via the first optical transmission. Detecting a pulserepetition interval of light pulses can be different from successfullyreceiving a data packet. For example, the optical receiver 215 candetect light and translate the light to an electronic signal. The device205 can compare a characteristic (e.g., voltage, current, or power) ofthe electronic signal with a threshold. If, responsive to thecomparison, the first device 205 determines that the electronic signalis greater than the threshold, the first device 205 can determine thatan optical transmission was received. However, even though the firstdevice 205 determines than an optical transmission was received, theoutput level of the optical transmission might be too low tosuccessfully interpret or parse one or more data packets or otherinformation carried by the optical transmission. For example, theintensity level of the optical transmission might be high enough todetermine that an optical transmission was received, but not high enoughto decipher or identify the bits carried via the optical transmission.While the first device 205 may not identify the data packet, the firstdevice 205 can determine that an optical transmission was received and apulse repetition interval or other parameter of the opticaltransmission. For example, the optical transmission can include 100light bursts or pulses over a time interval of one second, therebyhaving a pulse repetition interval of 0.01 milliseconds or a pulserepetition frequency of 100 Hz. The first device 205 can determine thatoptical transmissions with a pulse repetition interval of 0.01milliseconds is a default pulse repetition interval that indicates thatthe second device 255 did not successfully receive or determine thefirst one or more data packets transmitted in the first opticaltransmission.

If the link manager agent 220 of the first device 205 determines thatthe second device 255 did not successfully (or failed to) receive theone or more data packets carried via the first optical transmission, thelink manager agent 220 can transmit a second optical transmission at asecond output level. The second output level can be different, lessthan, or greater than the first output level. The second output levelcan be greater than the first output level if the first device 205determines that the second device 255 failed to receive the data packetsvia the first optical transmission. For example, the link manager agent220 of the first device 205 can instruct the optical transmitter 210 ofthe first device 205 to transmit the second optical transmission at agreater or lesser output level responsive to the second device 255receiving, parsing, decoding, or otherwise obtaining the data packetcarried via the first optical transmission. The second opticaltransmission can include a second data packet. The second data packetcan be the same as the first data packet, or different from the firstdata packet. The second data packet can be encoded or generated using aprotocol 250, such as the same protocol used to generate the first datapacket, or a different protocol. In some cases, the second opticaltransmission can be the same or similar to the first opticaltransmission, except for an optical transmission parameter such as lightintensity.

The link manager agent 220 of the first device 205 can determine whetherthe second device 255 (or link manager agent 220 of the second device255) received the second optical transmission carrying a second one ormore data packets. In some cases, the first device 205 can determinethat the second device 255 did not, or failed to, successfully receivethe second one or more packets of the second optical transmission. Insome cases, the first device 205 can determine that the second device255 successfully received the second one or more packets of the secondoptical transmission.

For example, the first device 205 can determine or identify that thesecond one or more packets were successfully received based on receivingoptical transmissions from the second device 255 at a secondpredetermined time interval that is different from the firstpredetermined time interval. For example, the first time interval caninclude a pulse repetition interval of 0.01 milliseconds and the secondtime interval can include a pulse repetition interval different from0.01 milliseconds, such as 0.02 milliseconds, 0.001 milliseconds, 0.002milliseconds, or some other pulse repetition interval.

The second device 255 can use one or more techniques to indicate thatthe second device 255 successfully received a data packet, such as theone or more second data packets of the second optical transmission. Forexample, a link manager agent 220 of the second device 255 (or secondlink manager agent 220) can stop or cease transmitting opticaltransmissions for a time interval to indicate successful receipt of thesecond data packet. Stopping or ceasing the transmission of opticaltransmissions or signals can reduce energy consumption by the seconddevice 255, while also indicating receipt of the second data packet. Forexample, the second device 255 (or link manager agent 220 of the seconddevice 255) can disable the second optical transmitter 210 of the seconddevice 255 responsive to the determination that the second link manageragent 220 successfully received the second packet. The second opticaltransmitter 210 of the second device 255 can be disabled to indicate tothe first link manager agent 220 of the first device 205 that the secondlink manager agent 220 of the second device 255 successfully receivedthe second packet. Disabling can refer to turning off, temporarilydisabling, disengaging, or entering a standby mode.

Thus, and in some embodiments, the first device 205 and the seconddevice 255 can utilize a half-duplex communication technique to identifythat the second packet was successfully received by the second linkmanager agent. The half-duplex technique can refer to a technique inwhich the second device can indicate successful receipt of the datapacket to the first device even though the first device may not havesuccessfully received a data packet from the second device. For example,the first link manager agent 220 of the first device 205 may determinethat the second packet was successfully received by the second linkmanager agent 220 of the second device 255 prior to the first linkmanager 220 of the first device 205 successfully receiving one or moredata packets via one or more optical transmissions from the second linkmanager agent 220 of the second device 255.

The first link manager agent 220 of the first device 205 can establish atransmission output level for the first device 205. The first linkmanager agent 220 can establish the transmission output level responsiveto identifying that one or more packets were successfully received bythe second device 255. The link manager agent 220 can establish thetransmission output level as the output level used to transmit theoptical transmission carrying the data packets that were successfullyreceived by the second device 255. For example, the first device 205 cantransmit packets at an output level, determine the packets weresuccessfully received, and then use the output level as the transmissionoutput level for subsequent optical transmissions to the second device255.

The first device 205 or second device 255 can include a gain controlunit 225. The gain control unit 225 can include an AGC unit 225 such asa receiver AGC unit 225. The AGC unit 225 can adjust a gain level basedon a measurement of at least one of an alternating current component ordirect current component of an electric signal that translates one ormore optical transmissions received by the first seismic dataacquisition unit. The electrical signal can be generated by the opticalreceiver 215 responsive to receiving the one or more opticaltransmissions. For example, the AGC unit 225 can receive the electricalsignals from the optical receiver 215, compare them with a threshold,and adjust the gain responsive to the threshold. The gain can refer toan amplification of the electrical signal. The amplified electricalsignal can be communicated or provided to one or more components of thedevice 205, including, e.g., the link manager agent 220 or other processof the device 205 or 255.

In some cases, the device 205 or 255 can include an overdrive protectionsystem 230. The overdrive protection system 230 can detect a signallevel greater than or equal to a threshold, and instruct a component inthe device 205 or 255 to disable or turn off responsive to detection ofthe signal level greater than or equal to the threshold. The overdriveprotection system 230 can access one or more thresholds stored in datastorage device 235, or be preconfigured with one or more thresholds. Theoverdrive protection system 230 can protect one or more components ofdevice 205 or 255 from overheating. The overdrive protection system 230can reduce battery usage or battery drain by reducing the amount ofpower consumed by the electrical components conveying the electricalsignals. The overdrive protection system 230 can include a circuit orother component configured to monitor one or more components of thedevice 205 or 255. If the overdrive protection system 230 detects adangerous condition, then the overdrive protection system 230 can turnoff, trip, or disable the one or more components of the device 205 or255. For example, the overdrive protection system 230 can detect asignal level greater than or equal to a threshold and, responsive todetection of the signal level greater than or equal to the threshold,turn off a receiver of the device.

Upon establishing the transmission output level, the first device 205can establish the optical link 260. In some cases, the optical link 260can be determined to be established upon both the first device 205 andthe second device 255 identifying the transmission output level at whichthe other of the first device 205 or the second device 255 successfullyreceives and processes a data packet carried by an optical transmission.

The second device 225 can establish a transmission output level similarto the technique used by the first device 205 to establish thetransmission output level. For example, the second link manager agent220 of the second device 255 can transmit, to the first link manageragent 220 of the first device 205, a third optical transmission at athird output level. The third optical transmission can include a thirdpacket corresponding to the network protocol. The second device 255 candetermine that the first link manager agent 220 of the first device 205failed to receive the third packet via the third optical transmission.The second device 255 can transmit, responsive to failure of the thirdoptical transmission, a fourth optical signal at a fourth output levelgreater than the third output level. The fourth optical transmission caninclude a fourth packet corresponding to the network protocol. Thesecond device 255 can identify that the fourth packet was successfullyreceived by the first link manager agent. The second device 255 canestablish responsive to a determination of successful receipt of thesecond packet and the fourth packet, an optical link 260 between thedevice 205 and the device 255.

Subsequent to establishing the optical link 260, the first device 205 orsecond device 255 can maintain the optical link 260. For example, thefirst link manager agent 220 of the first device 205 can provide, forinclusion in a third or subsequent optical transmission, status dataused to maintain a level of quality of the optical link. The status datacan include parameters or characteristics of the optical link 260 or acomponent, function or mode of the device 205 or 255. For example, thestatus data can include at least one of an automatic gain control value,receiver control setting, transmitter control setting, receiver clocklock, framing error, bit error, bit error rate, network packet errorsreceived, distance measurement, or packet retries.

Subsequent to establishing the link, the first device 205 or seconddevice 255 can adjust the established transmission output level based onthe status information. The status information can indicate a level ofquality of the optical link, such as poor, good, excellent (or low,medium, high, or a numeric value or grade). For example, if the qualityof the optical ink 260 is low, or the status information indicates anumber of network packet errors, framing error, bit error, or bit errorrate that is greater than or equal to a threshold, the device 205 ordevice 255 can determine to increase the transmission output level. Theincreased transmission output level may be responsive to a change in anenvironmental parameter of the free-space, such as a turbidity of thewater, or distance between the devices 255.

The link manager agent 220 can determine a distance between the firstdevice 205 and the second device 255. The link manager agent 220 candetermine the distance based on a phase error or phase shift in one ormore optical signals encoded with a repetitive signal. For example, thedevice 205 can encode a repetitive signal in the transmitted data thatis returned back the device 205 via device 255. The device 205 canmeasure the phase error to the source to determine the two-waypropagation time. The system can determine the distance using thetwo-way propagation time and the speed of the signal (e.g., speed oflight in free space). The device 205 can use the distance between atransmitter 210 of the first device 205 and receiver 215 of the seconddevice 255 that receives the signal transmitted by the transmitter 210of the first device 205 to control transmit levels and determine variousparameters or limits.

FIG. 3 is an embodiment of a system to manage an optical communicationlink in free-space. The system 300 can establish the opticalcommunications link, maintain the optical communications link, andprovide automatic gain control for a receiver 215. The system 300 caninclude one or more component, element or functionality of system 200.The system 300 can include a link manager agent 305. The link manageragent 305 can include one or more component or functionality of linkmanager agent 220. The link manager agent 305 can include or beconfigured with a transmit control component 310 and a receive controlcomponent 325. The transmit control component 310 can communicate orinteract with the receive control component 325. The transmit controlcomponent 310 can include a UDP transmit component 315 and a hardwarelayer 320. The UDP transmit component 315 can be designed andconstructed to transmit data packets using the UDP network protocol. TheUDP Transmit module 315 gathers status information about the variousstates of the local transmitter 210 and local receiver 215. Thesestatuses can include, for example, optical output level, optical receivequality, frame errors received, bit errors received, link locked, orother status. The status can then be formed into a UDP packet to be sentthe network stack 340 and then transmitted to the paired link manageragent 305 in the second device 255.

The hardware layer 320 can refer to a layer that interfaces with theoptical transmitter 210. The hardware layer 320 can be configured totransmit electronic signals or instructions to the optical transmitter210. The hardware layer 320 can perform a function of link management,such as establishing the link or maintaining the established link. Thehardware abstraction layer 320 can refer to layer of programming thatallows the link manager agent 305 to interact with a hardware device(e.g., optical transmitter 210) at a general or abstract level ratherthan at a detailed hardware level. The hardware abstraction layer 320allows the link manager agent 310 to gather information about thefunction of the optical transmitter 210. This information can include,for example, optical output level, output state such as on or off,transmit quality, or other information. Additionally, the hardwareabstraction layer 320 allows the link manager agent 310 to control theoptical transmitter 210 for the purpose of establishing and or maintainthe link 260.

The receive control component 325 can include a UDP receive component330 and a hardware layer 335. The UDP receive component 330 can bedesigned and constructed to receive or process data packets formed usingthe UDP network protocol. The hardware layer 335 can be configured toreceive electronic signals or instructions from the optical receiver215. The hardware layer 335 can perform a function of link management,such as establishing the link or maintaining the established link. Thehardware abstraction layer 335 can refer to layer of programming thatallows the link manager agent 305 to interact with a hardware device(e.g., optical receiver 215) at a general or abstract level rather thanat a detailed hardware level.

The UDP transmit component 315 and the UDP receive component 330 caninclude or communicate with or via respective network stacks 340 or 365,field programmable gate array (FPGA) devices 345 or 370, status 350 or375, data link layer 355 or 380, or physical layers 360 or 385. Thetransmit control component 310 can control, manage, or otherwisecommunicate with an optical transmitter 210. The receive controlcomponent 325 can control, manage, or otherwise communicate with anoptical receiver 215.

The network stacks 340 and 365 can refer to a protocol stack, such as acomputer networking protocol suite. The network stack 340 or 365 caninclude a software implementation of the definition of the protocols.The network stack 340 or 365 can be divided into different protocols(e.g., HTTP, TCP, IP, Ethernet, or IEEE 802.eu) or different layers(e.g., application layer, transport layer, internet/network layer, datalink/link layer, or physical layer). The network stack 340 and 365 referto a combination of hardware and software that implements Ethernetnetwork protocols (e.g., TCP, IP, or UDP). The network stack 340 canimplement the transmit side of the network used on link 260 and networkstack 365 can implement the receive side of the network used on link260. Network stack 340 transforms data from the transmit control 310 ofthe link manager agent 305 and into the requested packet type (e.g., UDPor TCP/IP) for transmission on link 260. Network stack 365 can receivedata packets in a standard form (e.g., UDP or TCP/IP) and deliver it tothe receive control 325 of link manager agent 305.

The data link layer 355 or 380 can refer to a second layer of theseven-layer OSI model of computer networking, or the network stack 340or 365. The data link layer 355 can include the protocol layer thattransfers data between adjacent network nodes in a network, such as awide area network (WAN) or between nodes on the same local area network(LAN) segment. The data link layer 355 or 380 can provide the functionaland procedural techniques to transfer data between network entities, aswell as detect and possibly correct errors that may occur in thephysical layer 360 or 385.

The data link layer 355 and 380 can refer to a combination of hardwareand software that implements data encoding for transmission on link 260as well as data buffering between network stack 340 and 365 and physicallayer 360 and 385. Data link layer 355 buffers data packets from networkstack 340 to allow for the necessary rate conversion between theinterface at the FPGA 345 and the desired signaling rate on link 260.Additionally, data link layer 355 encodes the data from network stack340 for transmission on link 260. The encoding can include, for example,8B/10B, 4B/5B, Manchester, phase-shift keying, or other encodings. Datalink layer 380 receives data from physical layer 385 and decodes thedata before sending it to network stack 365. Data link layer 380 canprovide status about decoding errors, framing errors, etc. to FPGA 370.In some implementations, data link layer 355 and 380 can use one or moreFPGAs 345 and 370 to implement the functions of the respective layers.

The physical layer 360 or 385 can refer to a physical layer in the OpenSystems Interconnection (“OSI”) model. The physical layer 360 or 385 caninteract with actual hardware (e.g., optical transmitter 210 or opticalreceiver 215) and signaling mechanism. Physical layer 360 or 385 canprovide physical connectivity of two different stations. The physicallayer 360 or 385 can defines the hardware equipment, cabling, wiring,frequencies, pulses used to represent binary signals, for example. Thephysical layer 360 or 385 can provides its services to the data-linklayer 355 or 380, respectively. The data-link layers 355 or 380 can handover frames to the physical layer 360 or 385. Physical layer 360 or 385can convert them to electrical pulses, which represent binary data. Thebinary data can be sent over a wired or wireless media. For example, thephysical layer 360 can convert binary data from the data link layer 355to an electrical or optical signal for transmission by the opticaltransmitter 210. In another example, physical layer 385 can convert anoptical or electrical signal received from optical receiver 215 to abinary signal to be provided to the data link layer 380.

The physical layer 360 and 385 can refer to a combination of hardwareand software that implements the data frame rate and transforms thatdata between a parallel form and a serial form for transmission on thelink 260. Physical Layer 360 takes data from data link layer 355 andconverts it from a parallel form to a serial form for transmission onlink 260. Additionally, physical layer 360 maintains the required idlepatterns when there is no data to be sent. This idle pattern is designedto keep the paired transmitter and receiver on link 260 clock locked andcan be used to determine low level status of the link. Physical layer385 converts received data from link 260 from a serial form to aparallel form and sends it to data link layer 380. Physical layer 385can recover the clock rate from the data modulation that is necessary toboth decode the received bits correctly and establish the proper framerate alignment for transforming the data from its received serial formto a parallel form. In some implementations, the physical layer 360 and385 can use one or more FPGAs 345 and 370 to implement the functions ofthe respective layers.

The status 350 and 375 can provide feedback on the function of data linklayer 355 and 380 as well as physical layer 360 and 385. This statusinformation can be available to link manager agent 305 and can be usedin establishing and then maintaining the link 260. Some or all of thestatus 375 can be passed from FPGA 370 to FPGA 345 and then transmittedover link 260 as low level information of establishing link 260.

The link manager agent 305 can perform receiver automatic gain control.The link manager agent 305 can perform receiver automatic gain controlby adjusting a parameter of the optical receiver 215 to an optimum orimproved condition based on, or in response to, the amount or level ofan incoming optical signal. For example, the link manager agent 305 canservo the receiver to an optimum condition given the amount of incomingoptical signal. The link manager agent 305 can servo the receivercontinuously or based on a time interval (e.g., 1 second, 10 seconds, 30seconds, 1 minute, 5 minutes, 1 millisecond, or a sample period). Thelink manager agent 305 can perform receiver automatic gain controlthrough the evaluation of the current control setting and themeasurements of both the AC and DC components of the incoming signal.The algorithm can evaluate the measurements and change the controlsetting appropriately. The link manager agent 305 can provide a signalquality indication to a higher link management layer that indicateswhether or if the signal is high (e.g., a signal level that can damage acomponent of the receiver, distorts the information or signal, or isabove a threshold) or the signal level is low (e.g., a signal level thatis too low for the receiver to detect or distorts the information orsignal), or if the signal level is within acceptable levels. Thereceiver automatic gain control technique can perform error recoveryfunctionality to handle the tripping of the overdrive protection circuitand return to normal operation.

The link manager agent 305 or system 300 can establish an opticalcommunications link in free space. Establishing the link may differ frommaintaining the link because when establishing the link, information maynot be sent (or successfully parsed or received) between the two linkmanager agents to control the link. To establish the link, the linkmanager agent 305 can use a half-duplex technique and the use of one ormore techniques on both sides of the link.

The system 300 can perform a transmitter optical output variationtechnique. For example, when initiating a link between two devices suchas 205 and 255, the link manager agents 305 or 220 of the respectivedevices can startup or initialize their respective optical transmitters210 at a first output (e.g., a low or lowest output level) andincrementally transition their outputs following a triangle wavepattern. This variation technique can stop, terminate, or completeresponsive to or upon receiving a successful UDP packet from the pairedlinked manager agents. Responsive to receiving the UDP packet, the linkmanager agents 305 can transition from link initiation to linkmaintenance. For example, reception of the UDP packet can signal thetransition from link initiation to link maintenance.

The system 300 can include, be configured with, or perform a transmitterout-of-band optical receive acknowledgement technique. The transmitterout-of-band optical receive acknowledgment technique can include ahalf-duplex communication technique designed to signal the transmittingagent (e.g., link manager agent 305) that the output transmission hasreached a normal or predetermined operating point. The signal can causeor instruct the link manager agent 305 to disable its output transmitterfor a half-second (or other fraction of a second or time interval) whenits receiver signals that it sees an acceptable signal level. Thishalf-duplex signaling technique can allow for adaptive changes in theoutput level controls prior to being able to receive the UDP packet thatsignals the completion of link initiation. Disable can refer to turningthe output transmitter off, putting the output transmitter in a standbyor low-power mode, disengaging the output transmitter, or temporarilydisabling (e.g., for a time period or in a manner that allows the outputtransmitter to be enabled or turned on) the output transmitter.

The system 300 can include, be configured with, or perform a techniquebased on a transmitter data link layer. For example, instead of or inaddition to using the transmitter output levels, the system can use thetransmitting data during the link initiation phase to create ahalf-duplex communication to the receiving agent. By embedding statusdata about the state of the received signal in the output signalpattern, the system 300 can determine the quality of the pairedtransmitter. The system can use this information to adjust the pairedtransmitter. Once both transmitter/receiver pairs have reached a normalor predetermined operation condition, the link initiation process cancomplete, and the link manger agents 305 can communicate directly withone another to maintain the link (e.g., link 260 depicted in FIG. 2).

The system 300 can include, be configured with, or perform a techniqueusing or based on a receiver data link layer. The system can maintain anestablished link by sending information over the link between the linkmanagement agents.

The system can use optical status packets to maintain the link 260. Forexample, the link manager agents 305 can use a UDP packet to communicatewith each other since UDP may not require acknowledgment of properreceipt. These packets can contain status information about one or boththe local transmitter and local receiver. This information can be usedto guide the control techniques of the link management agents andmaintain a predetermined or link quality that facilitates communicationof information. The information included in the packet can include, forexample: receiver AGC quality value, receiver and transmitter controlsettings, receiver clock lock, framing errors received (i.e. biterrors), network packet errors received, or distance measurement.

FIG. 4 depicts a method for managing an optical communication link infree-space. The method 400 can be performed by one or more component orelement of system 200, system 300 or system 500. At 405, a first devicetransmits a first optical transmission. For example, a link manageragent of the first device can instruct an optical transmitter of thefirst device to transmit a first optical transmission at a first outputlevel. The first output level can be an output intensity level forlight. The first device can transmit the optical transmission towards asecond device, or to a second link manager agent of the second device.The optical transmission can include, be encoded with, or otherwisecarry information such as a bit, byte, frame, packet, data packet, ornetwork packet.

At 410, the first device can determine a failure. For example, the firstdevice can determine that the second link manager agent of the seconddevice failed to receive the first packet via the first opticaltransmission. The first device can determine the failure based on aparameter or characteristic associated with one or more opticaltransmissions received by the first device subsequent to the firstdevice transmitting the first optical transmissions.

At 415, the first device can transmit a second optical transmission. Thefirst device can transmit the second optical transmission responsive tofailure of the first optical transmission. The first device can transmitthe second optical transmission responsive to determining that a datapacket of the first optical transmission was not successfully receivedby the second device. The first device can transmit the second opticaltransmission at a second output level greater than or less than thefirst output level used to transmit the first optical transmission. Thesecond optical transmission can include a second packet corresponding tothe network protocol.

At 420, the first device can identify a success. The first device canidentify that the second packet was successfully received by the secondlink manager agent. The first device can determine that the seconddevice successfully received one or more data packets in the secondoptical transmission based on the first device receiving a third opticaltransmission having a predetermined parameter or characteristicsubsequent to the second optical transmission.

The first device can identify that the second packet was successfullyreceived by the second device prior to the first device successfullyreceiving one or more data packets via one or more optical transmissionsfrom the second device. Thus, the first device can use a half-duplexcommunication technique to identify that the second packet wassuccessfully received by the second device.

At 425, the first device can establish an output level. For example, thefirst device can establish a transmission output level that correspondsto the second output level used to for the second optical transmissionthat was successfully received by the second device. The first devicecan establish the transmission output level responsive to theidentification that the second packet was successfully received.

The system can maintain the optical link that has been establishedbetween two devices. After the optical link has been established with afirst output level, the system can send subsequent opticaltransmissions, determine a quality of the optical link, and adjust theoutput level used for optical transmissions over the optical link if oneor more data packets are not successfully received. For example, a firstlink manager agent of a device can identify an optical link establishedwith a first output level between the device and a second link manageragent of a seismic data acquisition device. The first link manager agentcan transmit, to the second link manager agent of the seismic dataacquisition device, a first optical transmission at a first outputlevel. The first optical transmission can include a first packetcorresponding to a network protocol. The first link manager agent candetermine that the second link manager agent failed to receive the firstpacket via the first optical transmission. For example, the second linkmanager agent may not provide an indication or transmission in responseto receiving the packet because the second link manager did notsuccessfully receive the packet, where successful receipt can includesuccessfully parsing the packet to identify a payload or header of thepacket.

Responsive to failure of the first optical transmission, the first linkmanager agent can transmit a second optical signal at a second outputlevel greater than the first output level. The second opticaltransmission can include a second packet corresponding to the networkprotocol. The first link manager agent can identify that the secondpacket was successfully received by the second link manager agent. Thefirst link manager agent can adjust, responsive to a determination ofsuccessful receipt of the second packet, the optical link to use thesecond output level for optical transmissions between the device and theseismic data acquisition device.

One or both of the link manager can provide to the other link managerstatus data. For example, the second link manager can provide statusdata to the first link manager agent. The status data can be included ina third optical transmission to the first link manager agent. The statusdata can be used to maintain a level of quality of the optical link. Forexample, if the status data indicates a low quality level (e.g., below athreshold), then the output level can be adjusted. If the status dataindicates a high quality level above a threshold, then the output levelcan be lowered. The output level can be lowered responsive to the highquality level above the threshold, which can reduce battery usage orconsumption. The status data can include at least one of an automaticgain control value, receiver control setting, transmitter controlsetting, receiver clock lock, framing error, bit error, bit error rate,network packet errors received, distance measurement, or packet retries.The second link manager agent can adjust the output level of an opticaltransmitter of the seismic data acquisition device based on the level ofquality of the optical link.

FIG. 5 is a block diagram of a computer system 500 in accordance with anembodiment. The computer system or computing device 500 can be used toimplement one or more component of system 200 or system 300, or elementof method 400. The computing system 500 includes a bus 505 or othercommunication component for communicating information and a processor510 a-n or processing circuit coupled to the bus 505 for processinginformation. The computing system 500 can also include one or moreprocessors 510 or processing circuits coupled to the bus for processinginformation. The computing system 500 also includes main memory 515,such as a random access memory (RAM) or other dynamic storage device,coupled to the bus 505 for storing information, and instructions to beexecuted by the processor 510. Main memory 515 can also be used forstoring seismic data, binning function data, images, reports, tuningparameters, executable code, temporary variables, or other intermediateinformation during execution of instructions by the processor 510. Thecomputing system 500 may further include a read only memory (ROM) 520 orother static storage device coupled to the bus 505 for storing staticinformation and instructions for the processor 510. A storage device525, such as a solid state device, magnetic disk or optical disk, iscoupled to the bus 505 for persistently storing information andinstructions.

The computing system 500 may be coupled via the bus 505 to a display 535or display device, such as a liquid crystal display, or active matrixdisplay, for displaying information to a user. An input device 530, suchas a keyboard including alphanumeric and other keys, may be coupled tothe bus 505 for communicating information and command selections to theprocessor 510. The input device 530 can include a touch screen display535. The input device 530 can also include a cursor control, such as amouse, a trackball, or cursor direction keys, for communicatingdirection information and command selections to the processor 510 andfor controlling cursor movement on the display 535.

The processes, systems and methods described herein can be implementedby the computing system 500 in response to the processor 510 executingan arrangement of instructions contained in main memory 515. Suchinstructions can be read into main memory 515 from anothercomputer-readable medium, such as the storage device 525. Execution ofthe arrangement of instructions contained in main memory 515 causes thecomputing system 500 to perform the illustrative processes describedherein. One or more processors in a multi-processing arrangement mayalso be employed to execute the instructions contained in main memory515. In some embodiments, hard-wired circuitry may be used in place ofor in combination with software instructions to effect illustrativeimplementations. Thus, embodiments are not limited to any specificcombination of hardware circuitry and software.

Although an example computing system has been described in FIG. 5,embodiments of the subject matter and the functional operationsdescribed in this specification can be implemented in other types ofdigital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this specification andtheir structural equivalents, or in combinations of one or more of them.

Embodiments of the subject matter and the operations described in thisspecification can be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. The subject matter described inthis specification can be implemented as one or more computer programs,e.g., one or more circuits of computer program instructions, encoded onone or more computer storage media for execution by, or to control theoperation of, data processing apparatus. Alternatively or in addition,the program instructions can be encoded on an artificially generatedpropagated signal, e.g., a machine-generated electrical, optical, orelectromagnetic signal that is generated to encode information fortransmission to suitable receiver apparatus for execution by a dataprocessing apparatus. A computer storage medium can be, or be includedin, a computer-readable storage device, a computer-readable storagesubstrate, a random or serial access memory array or device, or acombination of one or more of them. Moreover, while a computer storagemedium is not a propagated signal, a computer storage medium can be asource or destination of computer program instructions encoded in anartificially generated propagated signal. The computer storage mediumcan also be, or be included in, one or more separate components or media(e.g., multiple CDs, disks, or other storage devices).

The operations described in this specification can be performed by adata processing apparatus on data stored on one or morecomputer-readable storage devices or received from other sources. Theterm “data processing apparatus” or “computing device” encompassesvarious apparatuses, devices, and machines for processing data,including by way of example a programmable processor, a computer, asystem on a chip, or multiple ones, or combinations of the foregoing.The apparatus can include special purpose logic circuitry, e.g., an FPGA(field programmable gate array) or an ASIC (application specificintegrated circuit). The apparatus can also include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, across-platform runtime environment, a virtual machine, or a combinationof one or more of them. The apparatus and execution environment canrealize various different computing model infrastructures, such as webservices, distributed computing and grid computing infrastructures.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a circuit, component, subroutine, object, orother unit suitable for use in a computing environment. A computerprogram may, but need not, correspond to a file in a file system. Aprogram can be stored in a portion of a file that holds other programsor data (e.g., one or more scripts stored in a markup languagedocument), in a single file dedicated to the program in question, or inmultiple coordinated files (e.g., files that store one or more circuits,subprograms, or portions of code). A computer program can be deployed tobe executed on one computer or on multiple computers that are located atone site or distributed across multiple sites and interconnected by acommunication network.

Processors suitable for the execution of a computer program include, byway of example, microprocessors, and any one or more processors of adigital computer. A processor can receive instructions and data from aread only memory or a random access memory or both. The elements of acomputer are a processor for performing actions in accordance withinstructions and one or more memory devices for storing instructions anddata. A computer can include, or be operatively coupled to receive datafrom or transfer data to, or both, one or more mass storage devices forstoring data, e.g., magnetic, magneto optical disks, or optical disks. Acomputer need not have such devices. Moreover, a computer can beembedded in another device, e.g., a personal digital assistant (PDA), aGlobal Positioning System (GPS) receiver, or a portable storage device(e.g., a universal serial bus (USB) flash drive), to name just a few.Devices suitable for storing computer program instructions and datainclude all forms of non-volatile memory, media and memory devices,including by way of example semiconductor memory devices, e.g., EPROM,EEPROM, and flash memory devices; magnetic disks, e.g., internal harddisks or removable disks; magneto optical disks; and CD ROM and DVD-ROMdisks. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

To provide for interaction with a user, implementations of the subjectmatter described in this specification can be implemented on a computerhaving a display device, e.g., a CRT (cathode ray tube) or LCD (liquidcrystal display) monitor, for displaying information to the user and akeyboard and a pointing device, e.g., a mouse or a trackball, by whichthe user can provide input to the computer. Other kinds of devices canbe used to provide for interaction with a user as well; for example,feedback provided to the user can be any form of sensory feedback, e.g.,visual feedback, auditory feedback, or tactile feedback; and input fromthe user can be received in any form, including acoustic, speech, ortactile input.

The above-described embodiments can be implemented in any of numerousways. For example, the embodiments may be implemented using hardware,software or a combination thereof. When implemented in software, thesoftware code can be executed on any suitable processor or collection ofprocessors, whether provided in a single computer or distributed amongmultiple computers.

Also, a computer may have one or more input and output devices. Thesedevices can be used, among other things, to present a user interface.Examples of output devices that can be used to provide a user interfaceinclude printers or display screens for visual presentation of outputand speakers or other sound generating devices for audible presentationof output. Examples of input devices that can be used for a userinterface include keyboards, and pointing devices, such as mice, touchpads, and digitizing tablets. As another example, a computer may receiveinput information through speech recognition or in other audible format.

Such computers may be interconnected by one or more networks in anysuitable form, including a local area network or a wide area network,such as an enterprise network, and intelligent network (IN) or theInternet. Such networks may be based on any suitable technology and mayoperate according to any suitable protocol and may include wirelessnetworks, wired networks or fiber optic networks.

A computer employed to implement at least a portion of the functionalitydescribed herein may comprise a memory, one or more processing units(also referred to herein simply as “processors”), one or morecommunication interfaces, one or more display units, and one or moreuser input devices. The memory may comprise any computer-readable media,and may store computer instructions (also referred to herein as“processor-executable instructions”) for implementing the variousfunctionalities described herein. The processing unit(s) may be used toexecute the instructions. The communication interface(s) may be coupledto a wired or wireless network, bus, or other communication means andmay therefore allow the computer to transmit communications to orreceive communications from other devices. The display unit(s) may beprovided, for example, to allow a user to view various information inconnection with execution of the instructions. The user input device(s)may be provided, for example, to allow the user to make manualadjustments, make selections, enter data or various other information,or interact in any of a variety of manners with the processor duringexecution of the instructions.

The various methods or processes outlined herein may be coded assoftware that is executable on one or more processors that employ anyone of a variety of operating systems or platforms. Additionally, suchsoftware may be written using any of a number of suitable programminglanguages or programming or scripting tools, and also may be compiled asexecutable machine language code or intermediate code that is executedon a framework or virtual machine.

In this respect, implementations can be embodied as a computer readablestorage medium (or multiple computer readable storage media) (e.g., acomputer memory, one or more floppy discs, compact discs, optical discs,magnetic tapes, flash memories, circuit configurations in FieldProgrammable Gate Arrays or other semiconductor devices, or othernon-transitory medium or tangible computer storage medium) encoded withone or more programs that, when executed on one or more computers orother processors, perform methods that implement the various embodimentsof the solution discussed above. The computer readable medium or mediacan be transportable, such that the program or programs stored thereoncan be loaded onto one or more different computers or other processorsto implement various aspects of the present solution as discussed above.

The terms “program” or “software” are used herein to refer to any typeof computer code or set of computer-executable instructions that can beemployed to program a computer or other processor to implement variousaspects of embodiments as discussed above. One or more computer programsthat when executed perform methods of the present solution need notreside on a single computer or processor, but may be distributed in amodular fashion amongst a number of different computers or processors toimplement various aspects of the present solution.

Computer-executable instructions may be in many forms, such as programmodules, executed by one or more computers or other devices. Programmodules can include routines, programs, objects, components, datastructures, or other components that perform particular tasks orimplement particular abstract data types. The functionality of theprogram modules can be combined or distributed as desired in variousembodiments.

Also, data structures may be stored in computer-readable media in anysuitable form. For simplicity of illustration, data structures may beshown to have fields that are related through location in the datastructure. Such relationships may likewise be achieved by assigningstorage for the fields with locations in a computer-readable medium thatconvey relationship between the fields. However, any suitable mechanismmay be used to establish a relationship between information in fields ofa data structure, including through the use of pointers, tags or othermechanisms that establish relationship between data elements.

Also, various implementations can be embodied as one or more methods, ofwhich an example has been provided. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.” References to“or” may be construed as inclusive so that any terms described using“or” may indicate any of a single, more than one, and all of thedescribed terms. References to at least one of a conjunctive list ofterms may be construed as an inclusive OR to indicate any of a single,more than one, and all of the described terms. For example, a referenceto “at least one of ‘A’ and ‘B’” can include only ‘A’, only ‘B’, as wellas both ‘A’ and ‘B’.

The phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including” “comprising” “having” “containing” “involving”“characterized by” “characterized in that” and variations thereofherein, is meant to encompass the items listed thereafter, equivalentsthereof, and additional items, as well as alternate implementationsconsisting of the items listed thereafter exclusively. In oneimplementation, the systems and methods described herein consist of one,each combination of more than one, or all of the described elements,acts, or components.

Where technical features in the drawings, detailed description or anyclaim are followed by reference identifiers, the reference signs havebeen included to increase the intelligibility of the drawings, detaileddescription, and claims. Accordingly, neither the reference identifiersnor their absence have any limiting effect on the scope of any claimelements.

The systems and methods described herein may be embodied in otherspecific forms without departing from the characteristics thereof. Theforegoing implementations are illustrative rather than limiting of thedescribed systems and methods. Scope of the systems and methodsdescribed herein is thus indicated by the appended claims, rather thanthe foregoing description, and changes that come within the meaning andrange of equivalency of the claims are embraced therein.

What is claimed is:
 1. A system to manage an optical link in free-spaceto communicate data via an aqueous medium, comprising: a seismic dataacquisition unit positioned on a seabed in the aqueous medium, theseismic data acquisition unit comprising: one or more sensors to detectacoustic waves that indicate subsurface lithologic formations orhydrocarbon deposits; a seismic data recorder to record seismic datacorresponding to the acoustic waves detected by the one or more sensors;and a first link manager agent of the seismic data acquisition unit to:receive, through the aqueous medium from a second link manager agent ofan underwater vehicle, a default optical transmission; transmit,responsive to receipt of the default optical transmission, through theaqueous medium to the second link manager agent of the underwatervehicle, a first optical transmission at a first output level, the firstoptical transmission comprising a first packet corresponding to anetwork protocol, the network protocol comprising at least one of a userdatagram protocol (UDP) and a transmission control protocol (TCP);receive, subsequent to transmission of the first optical transmission atthe first output level, one or more additional default transmissionsfrom the underwater vehicle having a same parameter as the defaultoptical transmission previously received from the underwater vehicle;determine, responsive to receipt of the one or more additional defaulttransmissions having the same parameter, that the second link manageragent failed to receive the first packet via the first opticaltransmission; transmit, responsive to failure of the first opticaltransmission, a second optical transmission at a second output leveldifferent than the first output level, the second optical transmissioncomprising a second packet corresponding to the network protocol;identify that the second packet was successfully received by the secondlink manager agent; and establish, responsive to the identification thatthe second packet was successfully received, the second output level asa transmission output level for the seismic data acquisition unit. 2.The system of claim 1, comprising: the first link manager agentconfigured to use a half-duplex communication technique to identify thatthe second packet was successfully received by the second link manageragent.
 3. The system of claim 1, comprising: the first link manageragent configured to identify that the second packet was successfullyreceived by the second link manager agent prior to successful receipt bythe first link manager agent of one or more data packets via one or moreoptical transmissions from the second link manager agent.
 4. The systemof claim 1, comprising: the second link manager agent configured todisable an optical transmitter of the seismic data acquisition deviceresponsive to the determination that the second link manager agentsuccessfully received the second packet, the optical transmitterdisabled to indicate to the first link manager agent that the secondlink manager agent successfully received the second packet.
 5. Thesystem of claim 1, comprising: the first link manager agent of theseismic data acquisition unit to determine, based on one or more opticalsignals comprising at least a portion of at least one of the firstoptical transmission and the second optical transmission transmittedbetween the seismic data acquisition unit and the underwater vehicle, adistance between the seismic data acquisition unit and the underwatervehicle based on a phase error in the one or more optical signalsencoded with a repetitive signal.
 6. The system of claim 1, comprising:the first link manager agent of the seismic data acquisition unitconfigured to: determine that the second link manager agent failed toreceive the first packet via the first optical transmission based onreceipt by the seismic data acquisition unit of a first one or moreoptical transmissions from the underwater vehicle at a firstpredetermined time interval; and identify that the second packet wassuccessfully received by the second link manager agent based on receiptby the seismic data acquisition unit of a second one or more opticaltransmissions from the underwater vehicle at a second predetermined timeinterval, the second predetermined time interval different from thefirst predetermined time interval.
 7. The system of claim 1, comprising:an automatic gain control unit of the seismic data acquisition unit toadjust a gain level based on a measurement of at least one of analternating current component or direct current component of one or moreoptical transmissions received by the seismic data acquisition unit. 8.The system of claim 1, comprising: an automatic gain control unit of theseismic data acquisition unit to increase a gain level based on ameasurement of at least one of an alternating current component ordirect current component of one or more optical transmissions receivedby the seismic data acquisition unit; an overdrive protection system ofthe seismic data acquisition unit to detect a signal level greater thanor equal to a threshold and, responsive to detection of the signal levelgreater than or equal to the threshold, turn off a receiver of theseismic data acquisition unit.
 9. The system of claim 1, wherein thesecond packet comprises a structure that corresponds to a user datagramprotocol.
 10. The system of claim 1, comprising: the first link manageragent configured to increase the first output level to the second outputlevel in accordance with a triangle wave pattern.
 11. The system ofclaim 1, comprising: the second link manager agent of the underwatervehicle configured to: transmit to the first link manager agent of theseismic data acquisition unit, a third optical transmission at a thirdoutput level, the third optical transmission comprising a third packetcorresponding to the network protocol; determine that the first linkmanager agent failed to receive the third packet via the third opticaltransmission; transmit, responsive to failure of the third opticaltransmission, a fourth optical transmission at a fourth output leveldifferent than the third output level, the fourth optical transmissioncomprising a fourth packet corresponding to the network protocol;identify that the fourth packet was successfully received by the firstlink manager agent; and establish responsive to a determination ofsuccessful receipt of the second packet and the fourth packet, theoptical link between the underwater vehicle and the seismic dataacquisition unit.
 12. The system of claim 1, comprising: the first linkmanager agent and the second link manager agent configured to establishthe optical link between the underwater vehicle and the seismic dataacquisition unit; and the first link manager agent configured toprovide, for inclusion in a third optical transmission, status data usedto maintain a level of quality of the optical link, the status datacomprising at least one of an automatic gain control value, receivercontrol setting, transmitter control setting, receiver clock lock,framing error, bit error, bit error rate, network packet errorsreceived, distance measurement, or packet retries.
 13. The system ofclaim 1, comprising: the first link manager agent and the second linkmanager agent configured to establish the optical link between theunderwater vehicle and the seismic data acquisition unit; the first linkmanager agent configured to provide, for inclusion in a third opticaltransmission, status data used to maintain a level of quality of theoptical link, the status data comprising at least one of an automaticgain control value, receiver control setting, transmitter controlsetting, receiver clock lock, framing error, bit error, bit error rate,network packet errors received, distance measurement, or packet retries;and the second link manager agent configured to adjust an output levelof an optical transmitter of the underwater vehicle based on the levelof quality of the optical link.
 14. The system of claim 1, wherein theunderwater vehicle comprises one of a remotely operated underwatervehicle or an autonomous underwater vehicle.
 15. A method of managing anoptical link in free-space to communicate data via an aqueous medium,comprising: providing a seismic data acquisition unit on a seabed in theaqueous medium, the seismic data acquisition unit comprising one or moresensors to detect acoustic waves that indicate subsurface lithologicformations or hydrocarbon deposits, and a seismic data recorder torecord seismic data corresponding to the acoustic waves detected by theone or more sensors; receiving, by a first link manager agent of theseismic data acquisition unit, through the aqueous medium from a secondlink manager agent of an underwater vehicle, a default opticaltransmission; transmitting, by the first link manager agent of theseismic data acquisition unit responsive to receipt of the defaultoptical transmission, through the aqueous medium, to the second linkmanager agent of the underwater vehicle, a first optical transmission ata first output level, the first optical transmission comprising a firstpacket corresponding to a network protocol, the network protocolcomprising at least one of a user datagram protocol (UDP) and atransmission control protocol (TCP); receiving, by the first linkmanager agent of the seismic data acquisition unit subsequent totransmission of the first optical transmission at the first outputlevel, one or more additional default transmissions from the underwatervehicle having a same parameter as the default optical transmissionpreviously received from the underwater vehicle; determining, by thefirst link manager agent, responsive to receipt of the one or moreadditional default transmissions having the same parameter, that thesecond link manager agent failed to receive the first packet via thefirst optical transmission; transmitting, by the first link manageragent responsive to failure of the first optical transmission, a secondoptical transmission at a second output level different than the firstoutput level, the second optical transmission comprising a second packetcorresponding to the network protocol; identifying, by the first linkmanager agent, that the second packet was successfully received by thesecond link manager agent; and establishing, by the first link manageragent responsive to determining that the second packet was successfullyreceived, the second output level as a transmitting output level for theseismic data acquisition unit.
 16. The method of claim 15, comprising:using a half-duplex communication technique to identify that the secondpacket was successfully received by the second link manager agent. 17.The method of claim 15, comprising: identifying, by the first linkmanager agent, that the second packet was successfully received by thesecond link manager agent prior to the first link manager agentsuccessfully receiving one or more data packets via one or more opticaltransmissions from the second link manager agent.
 18. The method ofclaim 15, comprising: turning off, by the second link manager agent, anoptical transmitter of the underwater vehicle responsive to determiningthat the second link manager agent successfully received the secondpacket, the second link manager agent disabling the optical transmitterto indicate to the first link manager agent that the second link manageragent successfully received the second packet.
 19. The method of claim15, wherein the underwater vehicle comprises one of a remotely operatedunderwater vehicle or an autonomous underwater vehicle.
 20. A method ofmanaging an optical link in free-space to communicate data via anaqueous medium, comprising: providing a seismic data acquisition unit ona seabed in the aqueous medium, the seismic data acquisition unitcomprising one or more sensors to detect acoustic waves that indicatesubsurface lithologic formations or hydrocarbon deposits, and a seismicdata recorder to record seismic data corresponding to the acoustic wavesdetected by the one or more sensors; identifying, by a first linkmanager agent of an underwater vehicle, the optical link established infree-space through the aqueous medium with a first output level betweenthe underwater vehicle and a second link manager agent of the seismicdata acquisition unit; receiving, by the first link manager agent of theunderwater vehicle, through the aqueous medium from a second linkmanager agent of seismic data acquisition unit, a default opticaltransmission; transmitting, by the first link manager agent, to thesecond link manager agent of the seismic data acquisition unit, a firstoptical transmission at the first output level, the first opticaltransmission comprising a first packet corresponding to a networkprotocol, the network protocol comprising at least one of a userdatagram protocol (UDP) and a transmission control protocol (TCP);receiving, by the first link manager agent of the underwater vehiclesubsequent to transmission of the first optical transmission at thefirst output level, one or more additional default transmissions fromthe seismic data acquisition unit having a same parameter as the defaultoptical transmission previously received from the seismic dataacquisition unit; determining, by the first link manager agent,responsive to receipt of the one or more additional defaulttransmissions having the same parameter, that the second link manageragent failed to receive the first packet via the first opticaltransmission; transmitting, by the first link manager agent responsiveto failure of the first optical transmission, a second opticaltransmission at a second output level different than the first outputlevel, the second optical transmission comprising a second packetcorresponding to the network protocol; identifying, by the first linkmanager agent, that the second packet was successfully received by thesecond link manager agent; and adjusting, by the first link manageragent responsive to a determination of successful receipt of the secondpacket, the optical link to use the second output level for opticaltransmissions between the underwater vehicle and the seismic dataacquisition unit.
 21. The method of claim 20, comprising: providing, bythe second link manager agent, for inclusion in a third opticaltransmission to the first link manager agent, status data used tomaintain a level of quality of the optical link, the status datacomprising at least one of an automatic gain control value, receivercontrol setting, transmitter control setting, receiver clock lock,framing error, bit error, bit error rate, network packet errorsreceived, distance measurement, or packet retries.
 22. The method ofclaim 20, comprising: providing, by the first link manager agent, forinclusion in a third optical transmission to the second link manageragent, status data used to maintain a level of quality of the opticallink, the status data comprising at least one of an automatic gaincontrol value, receiver control setting, transmitter control setting,receiver clock lock, framing error, bit error, bit error rate, networkpacket errors received, distance measurement, or packet retries; andadjusting, by the second link manager agent, output level of an opticaltransmitter of the seismic data acquisition device based on the level ofquality of the optical link.